The present invention relates to a sensing apparatus capable of adjusting a sensor output to a target value.
To detect physical quantities such as pressure and acceleration, highly accurate sensors are recently required.
However, in the manufacturing processes of the sensing apparatus, the sensing element is subjected to various stresses (including thermal stresses). Thus, it is inevitable that the sensor output deviates from a predetermined design (or target) value. In other words, individual sensing apparatuses, after being manufactured, have sensor outputs inherently different from each other. In this respect, the sensor output is not accurate.
A conventional sensing apparatus includes a memory circuit which stores quantized data for sensor characteristics adjustment and an adjusting circuit which adjusts the sensor output to a target value based on the quantized data read out from the memory.
The quantized data for sensor characteristics adjustment are written to the memory circuit after the assembling processes of the sensing apparatus are completely finished.
Furthermore, to use or incorporate the sensing apparatus in an automotive vehicle, it is necessary to check the reliability and durability of the sensing apparatus in severe circumstances. To this end, the manufactured sensing apparatuses are usually inspected through high-temperature and low-temperature environment tests in addition to an ordinary room-temperature environment test.
The sensor output may deviate due to the influence of thermal hysteresis caused by the above-described high-temperature or low-temperature inspections.
Moreover, the sensor output of a highly sensitive sensing apparatus may cause a deviation due to delicate thermal hysteresis (regardless of execution of severe environment tests) or an installation stress (which may arise in the hardening process of an adhesive used to bond the sensing element).
In view of the foregoing, it is difficult to assure a sufficiently high sensor output.
An object of the present invention is to provide a sensing apparatus which is capable of generating a reliable and accurate sensor output.
In order to accomplish this and other related objects, the present invention provides a sensing apparatus comprising a sensing element for detecting a predetermined physical quantity and generating a sensor signal, a signal processing circuit for processing the sensor signal and generating an output signal, a first memory circuit for storing characteristics control data used for adjusting sensor output characteristics, an adjusting circuit for performing an adjustment of sensor characteristics based on the characteristics control data stored in the first memory circuit, and a second memory circuit for storing fine control data used in a fine adjustment performed to correct a deviation resulting after the adjustment based on the characteristics control data stored in the first memory circuit.
According to the circuit arrangement of the present invention, the signal processing circuit generates the output signal representing the sensor signal produced from the sensing element. The adjusting circuit performs the sensor characteristics adjustment based on the characteristics control data stored in the first memory circuit so as to adjust the sensor output to the target value.
Thus, after finishing a series of assembling processes of the sensing apparatus, it becomes possible to equalize the output signal level to the target value with reference to the characteristics control data stored in advance in the first memory circuit. The sensing accuracy is improved.
Furthermore, in addition to the first memory circuit, the present invention provides the second memory circuit which stores the fine control data used in a fine adjustment performed to correct a deviation resulting after the adjustment based on the characteristics control data stored in the first memory circuit.
For example, when the sensor output signal deviates largely from the target value, the fine control data is written to the second memory circuit so as to eliminate the deviation.
Accordingly, the present invention makes it possible to exclude or eliminate various deviations in the sensor output which are usually caused in the manufacturing processes. The sensor characteristics can be easily and surely optimized before shipping the sensing apparatus. This sufficiently increases the accuracy and reliability of the sensor output. The required memory size of the second memory circuit is quite small. The overall cost of the system can be reduced.
Preferably, the first memory circuit and the second memory circuit are separately arranged so that circuit elements of the first memory circuit are independent of circuit elements of the second memory circuit.
Preferably, an add-subtract circuit is provided for selectively adding or subtracting the fine control data stored in the second memory circuit to or from the characteristics control data stored in the first memory circuit.
Preferably, the memory size of the second memory circuit is smaller than that of the first memory circuit.
Another aspect of the present invention provides a first method for adjusting sensing characteristics of a sensing apparatus.
First of all, characteristics control data is stored in a first memory for adjusting sensor output characteristics. In the next step, sensor characteristics of the sensing apparatus is adjusted based on the characteristics control data stored in the first memory so as to equalize a sensor output to a target value. When the sensor output deviates from the target value, the fine control data is stored in a second memory. Then, a fine adjustment of the sensor characteristics is performed based on the fine control data stored in the second memory so as to eliminate a deviation of the sensor output from the target value.
Another aspect of the present invention provides a second method for adjusting sensing characteristics of a sensing apparatus.
In a first step, characteristics control data is stored in a main memory for adjusting sensor output characteristics. In a second step, sensor characteristics is adjusted based on the characteristics control data stored in the main memory so as to equalize a sensor output of the sensing apparatus to a target value. In a third step, a predetermined performance test is performed for shipment of the sensing apparatus. In a fourth step, it is checked whether the sensor output of the sensing apparatus remains within an allowable range with respect to the target value even after finishing the performance test. In a fifth step, fine control data is stored in an auxiliary memory when the sensor output is not within the allowable range. Finally, in a sixth step, a fine adjustment of the sensor characteristics is performed based on the fine control data stored-in the auxiliary memory so as to eliminate a deviation of the sensor output from the target value.
In the above first and second adjusting methods, it is preferable that the second (or auxiliary) memory is independent of the first (or main) memory. The fine control data stored in the second (or auxiliary) memory is selectively added or subtracted to or from the characteristics control data stored in the first (main) memory. The memory size of the second (auxiliary) memory is smaller than that of the first (main) memory.